With air traffic increasing non-stop since its beginnings, the workload of and the number of tasks to be performed by air traffic controllers are increasing accordingly.
It is necessary to improve the flight procedures of aircraft flight plans, so as to best manage the available airspace, as well as the available equipment, such as landing runways.
This increase in air traffic compels, for example, increased frequencies of landing on landing runways. This entails notably the instigation of time constraints and maximum reduction in the time interval separating two successive landings on a runway, while maintaining a safety separation distance between the aircraft in the final approach so as to reduce the risks of collision or stalling related to wake turbulence or to unforeseen maneuvers such as go-arounds.
A flight plan is the detailed description of the route to be followed by an aircraft within the framework of a scheduled flight. It comprises notably a chronological sequence of waypoints described by their position, their altitude and their time of overflight. The waypoints constitute the reference trajectory to be followed by the aircraft with a view to best complying with its flight plan. This trajectory is a valuable aid both to the ground control personnel and to the pilot, for anticipating the movements of the aircraft, for example an airplane, and thus ensuring an optimum safety level, notably within the framework of the maintaining of inter-aircraft separation criteria. The flight plan is commonly managed aboard civilian airplanes by a flight management system designated by the terminology “Flight Management System”, that will be called FMS subsequently, which places the reference trajectory at the disposal of the flight personnel and at the disposal of the other onboard systems. Essentially with a view to safety, it is therefore necessary to ensure that the aircraft follows at least in geographical terms the reference trajectory described in the flight plan, so as notably to maintain separation distances between aircraft.
With this aim, State bodies and airport authorities have for example for a very long time been obliged to publish takeoff and landing procedures. These procedures were for a long time published solely in paper form, according to graphical and textual formalisms. They guarantee the safety of flights on departure or on arrival at aerodromes. But with the advent in avionics of flight management systems such as FMSs and navigation and landing units known by the terminology of “Global Navigation and Landing Unit” or GNLU, procedures published in paper form have become unsuitable, or indeed totally outmoded. The need has appeared to manage in a digital format all the procedures published by State bodies.
At present, the published procedures are supplied to various suppliers of navigation databases by specialized bodies of the States belonging to the International Civil Aviation Organization or ICAO. The textual and graphical formalisms used are defined by the ICAO, but sometimes they are poorly complied with by State bodies. The suppliers transform the textual descriptions into series of “legs” according to the terminology employed in the realm of aeronautics. A “leg” corresponds to a trajectory portion defined by several parameters, such as for example directives to be followed in terms of position, altitude, heading or route. Hereinafter in the present application, the terminology of “legs” will be replaced by the terminology of “trajectory portions” or “segments”, it being understood that this substitution is of interest only for translation purposes and that an English version of the present application ought preferably to preserve the original term of “leg”. In any event, the term “segment” must not here be considered as limited to straight line segments, it can also designate curvilinear segments or combinations of straight line segments and curvilinear segments. The ARINC 424 standard defines a segment or “leg” by parameters representing a point and the manner of arriving there.
The series of “legs” or of “segments” are supplied in a digital format, the suppliers being relatively free in their interpretation of the procedures published as series of segments. The databases thus produced by the suppliers are called navigation databases.
FIG. 1 illustrates an architecture of a flight management system. It is recalled that an aircraft is equipped with a flight management system, or FMS, which exchanges diverse information with the ground and with other equipment of the aircraft. It communicates with the crew by way of man-machine interfaces or MMIs, such as screens and keyboards. The navigation aid system assists the crew in the programming of the flight plan before takeoff up to landing. Its assistance in the programming of the flight plan consists on the one hand in plotting in the horizontal and vertical planes a trajectory skeleton formed of a succession of waypoints or WPs, associated with various directives regarding altitude, speed, heading etc., and on the other hand in calculating, also in the horizontal and vertical planes, the trajectory that the aircraft will have to follow in order to fulfill its mission.
When preparing for flight plan programming, the crew enter into the flight management system FMS, in an implicit or explicit manner, the geographical coordinates of the waypoints and the flight directives which are associated therewith, and obtain a trajectory skeleton, a flight trajectory and a flight plan from the flight management system FMS. The trajectory is constructed by chaining together segments linking the waypoints WP pairwise from the departure point to the destination point, at one and the same time to ensure the transitions of heading between segments at the level of the waypoints WP and to follow certain curved segments. The trajectory skeleton and the trajectory are displayed on a navigation screen so as to enable the crew to verify their relevance. The flight plan comprises the horizontal and vertical trajectories supplemented with the flight directives or clearances. The vertical trajectory is generally designated vertical profile.
Before takeoff, the flight plan aboard the aircraft and that of the air traffic control authority or ATC are identical.
During the flight, unforeseen events arise which will modify the flight plan. These involve for example changes of weather, of traffic, or indeed faults aboard the aircraft. These events are communicated to the ATC air traffic control authority when the latter is unaware thereof. The ATC can then transmit new flight directives taking these events into account and of which the crew are made aware by way of the man-machine interfaces MMI.
The onboard flight management system (FMS) determines the geometry of the 4D profile (3D+time-profile of speeds), and dispatches the guidance directives for following this profile to the pilot or to the automatic pilot AP. The following functions described in the ARINC 702 standard (Advanced Flight Management Computer System, December 1996) are at the disposal of a flight management system. Such a flight management system FMS comprises:                a navigation module LOCNAV, for performing optimal location of the aircraft as a function of the geo location means GL (GPS, GALILEO, VHF radio beacons, inertial platforms);        a flight plan module FPLN, for inputting the geographical elements constituting the skeleton of the route to be followed (departure and arrival procedures, waypoints WP);        a navigation database NAV_DB, for formulating geographical routes and procedures with the help of data included in the bases (points, beacons, segments, etc.);        a performance database, PERF_DB, containing the aircraft's aerodynamic and engine parameters;        a lateral trajectory module TRAJ, for formulating a continuous trajectory on the basis of the points of the flight plan, complying with the performance of the aircraft and the confinement constraints;        a prediction module PRED, for formulating an optimized vertical profile on the lateral trajectory;        a guidance module, GUID, for guiding in the lateral and vertical planes the aircraft on its 3D trajectory, while optimizing its speed;        a situation perception module SA, for “situation awareness”, notably for communicating with the ATC control centers and the other aircraft.        
At present, when the pilot modifies the trajectory of the aircraft, i.e. if the aircraft no longer follows its flight plan, the latter is not reupdated automatically. The onboard systems of aircraft, such as the flight management system FMS, make the assumption that the airplane returns to its trajectory according to a rejoining mode defined by the constructors of flight management systems FMS.
These systems make their predictions (altitude, time, speed, fuel consumed, etc.) over the whole set of points of the flight plan. These systems do not know how to filter a part of the flight plan in order to shorten it and to make predictions over a subset of elements of the initial flight plan.